.gamma.-methacryloxypropylsilane compounds such as .gamma.-methacryloxypropyltrimethoxysilane, and .gamma.-methacryloxypropyltriethoxysilane have a hydrolyzable group reacting with inorganic substances as well as an organic functional group in a molecule, and are widely used as coupling agents.
As a process for the preparation of such .gamma.-methacryloxypropylsilane compounds as mentioned above, it is known to allow to react, for example, allyl methacrylate with trichlorosilane in the presence of a platinum catalyst and isolate .gamma.-methacryloxypropyltrialkoxysilane as a product from the reaction mixture after treatment with alcohol.
In this process, however, corrosive hydrogen chloride is formed during the .gamma.-methacryloxypropylalkoxysilane synthesis. This process, therefore, involves such disadvantages that the removal of the hydrogen chloride is indispensable for carrying out the process and the chlorine content in the end product increases.
As a process for the preparation of .gamma.-methacryloxypropylsilane compounds, in which no removal of hydrogen chloride is required and there is no fear of increasing the chlorine content in the end product, it is known to allow allyl methacrylate to react with a hydrosilane compound such as trialkoxysilane or the like in one stage (hydrosilyl reaction) in the presence of a platinum based catalyst, and purify the reaction mixture by distillation.
In the process as mentioned above, however, there was involved such disadvantages that gelation of the reaction mixture or product is caused by polymerization of the material, i.e. an allyl methacrylate during the course of reaction, or polymerization of the reaction product, i.e. a .gamma.-methacryloxypropylsilane compound during the course of purification thereof. By virtue of such gelation as will occur in the reaction system and during the purification, the yield of the .gamma.-methacryloxypropylsilane compound will decrease and it becomes difficult to isolate efficiently the .gamma.-methacryloxypropylsilane compound from the reaction mixture containing the gel, because the gel once formed is sparingly soluble in the solvent and difficult to remove.
Under such circumstances, there has been proposed a process intended to inhibit the formation of the gel as aforesaid, wherein a hydrosilane compound and allyl methacrylate are added simultaneously to a toluene solution containing 2,5-di-t-butylhydroquinone as a polymerization inhibitor and a chloroplatinic acid solution as a catalyst (see U.S. Pat. No. 3,258,477). However, this process was economically disadvantageous in that large amounts of toluene as the solvent must be used.
Furthermore, there have heretofore been proposed various processes aiming at preventing the gel formation by using diverse polymerization inhibitors, for example, phenol compounds such as hindered phenol, aromatic amine compounds such as diphenylenediamine, or aromatic sulfur compounds such as phenothiazine (see, for example, Japanese Patent Laid-Open Nos. 283983/1987 and 188689/1988). However, no sufficient prevention of the gel formation in the reaction system and during the course of purification of the reaction mixture by distillation was achieved yet, and there is a strong and growing demand for a process capable of preventing effectively the gel formation as mentioned above.